Dielectric behaviour and pyroelectricity in SBN70-PVC composites

Abstract

Dielectric relaxation of the composites of 0–3 connectivity, made from Sr0.7Ba0.3Nb2O6 (SBN70) ceramic powder and poly(vinyl chloride) (PVC), with the volume fraction of ceramics Φ up to 0.2 was investigated in frequency range 100 Hz–1 MHz and temperature range 100–450 K. The SBN70-PVC composites samples were prepared from ceramic and polymer powders by hot-pressing method. The SBN70 ceramics was prepared by a sol-gel route. The microstructure of the powders was observed and the grain size was estimated using Hitachi S-4700 scanning electron microscope (SEM). The investigations of the pyroelectric response were performed using a modified, computer controlled Chynoweth method at room temperature a few months after poling. The SBN70 ceramics modifies the dielectric properties of the PVC polymer: (i) it increases the value of dielectric permittivity of the composites in the whole temperature range, (ii) the composite displays a maximum of the permittivity coming from dielectric anomaly of the ceramics. The addition of the ceramics weakly influences the dynamics of the polymer dielectric relaxation α described by Vogel--Fulcher model. The value of the pyroelectric coefficient p of poled composites increases with volume fraction of SBN70 ceramics. The p for composites with the Φ = 0.2 at modulation frequency of 1 Hz is about 100 µC m−2 K−1.